The ItemsPanelTemplate specifies the panel that is used for the layout of items. GroupStyle has a Panel property that is of type ItemsPanelTemplate. ItemsControl types have an ItemsPanel property that is of type ItemsPanelTemplate.

The following example uses a ControlTemplate to create a horizontal ListBox that has rounded corners. Note that in this example, instead of setting the ItemsPanel property as in previous example, the horizontal StackPanel is specified within the ControlTemplate. Note that the IsItemsHost property is set to true on the StackPanel, indicating that the generated items should go in the panel. When you specify it this way, the ItemsPanel cannot be replaced by the user of the control without using a ControlTemplate. Therefore, only do this if you know you wouldn't want the panel to be replaced without the use of a template.

Alternatively, you can do the following to achieve the same results. In this case, the ItemsPresenter creates the panel for the layout of the items based on what is specified by the ItemsPanelTemplate.